The control card logic circuitry allows for the addition of
option modules for synchronizing the following types of
software:
•
Control
•
Serial communications
•
Additional relays
•
Cascade pump controller
•
custom operating
3.2.2 Logic to Power Interface
The logic to power interface isolates the high-voltage
components of the power section from the low voltage
signals of the logic section. The interface section consists
of the power card and gate drive card.
The control card handles much of the fault processing for
output short circuit and ground fault conditions. The
power card provides conditioning of these signals. The
control card also handles scaling of current and voltage
feedback.
The power card contains a switch mode power supply
(SMPS), which provides the unit with 24 V DC, (+) 18 V DC,
(–) 18 V DC and 5 V DC operating voltage. The SMPS
powers the logic and interface circuitry. The SMPS is
supplied by the DC bus voltage. The adjustable frequency
drives can be purchased with an optional secondary SMPS,
which is powered from a customer supplied 24 V DC
source. This secondary SMPS provides power to the logic
circuitry with main input disconnected. It can keep units
with communication options live on a network when the
adjustable frequency drive is not powered from line power.
Circuitry for controlling the speed of the cooling fans is
also provided on the power card.
The gate drive signals from the control card to the output
transistors (IGBTs) are isolated and buffered on the gate
drive card. In units that have the dynamic brake option,
the driver circuits for the brake transistors are also on this
card.
3.2.3 Power Section
The high-voltage power section consists of AC input and
motor output terminals, fuses, wiring harness, AC and DC
bus bars, and optional components. The power section
(see
) also contains circuitry for the SCR/diode
modules in the rectifier; the DC bus filter circuitry
containing the DC coils, often referred to as the
intermediate or DC bus circuit; and the output IGBT
modules, which make up the inverter section.
The inrush circuit controls the firing of the SCRs in the
rectifier. When power is applied, the SCRs limit the
charging rate of the DC capacitors. Once the capacitors are
charged, the inrush circuit sequences the firing of the SCRs
to maintain the proper charge on the DC capacitors.
The DC bus circuitry regulates the pulsating DC voltage
created by the input AC supply.
The DC coil is a single unit with two coils wound on a
common core. One coil resides in the positive side of the
DC bus and the other in the negative. The coil aids in the
reduction of line harmonics.
The DC bus capacitors are arranged into a capacitor bank
along with bleeder and balancing circuitry.
The inverter section is made up of six IGBTs, commonly
referred to as switches. One switch is necessary for each
half phase of the three-phase power, for a total of six. The
six IGBTs are contained in three modules with two in each,
one positive (+) and one negative (-) for each phase.
A Hall effect type current sensor is on each phase of the
output to measure motor current. This type of device is
used instead of more common current transformer (CT)
devices to reduce the amount of frequency and phase
distortion that CTs introduce into the signal. With Hall
sensors, the average, peak, and ground leakage currents
can be monitored.
Internal Adjustable Frequen...
Service Manual
MG94A222
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
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Summary of Contents for VLT FC 103
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